Treatment of hydrocarbons



Jan. 30, 1940. w. E. KUHN TREATMENT OF HYDROCARBKONS Filed July 20, 1957 Patented Jan. 30, 194()Y UNITED srmes PATENT oFFlcr.

by mesne assignments, Corporation, New York,

Delaware to Texaco Development N. Y., a corporation of Application July 20, 1937, Serial No. 154,531

Y 3 Claims. This invention lrelates tothe treatment of hydrocarbon oils to produce therefrom lowerboiling hydrocarbon oils including motor-fuel constituents. More particularly, the invention relates to the treatment of a plurality of hydrocarbon oils of differing boiling ranges to produce therefrom motor-fuel constituents of high anti-knock value under conditions of highest eiliciency.

It is an object of the present invention to provide a method of treating a plurality of hydrocarbon oils of differing boiling ranges, and intermediate products' fromisaid hydrocarbon oils, under 4optimum conditions for each different oil whereby maximum conversion to motor fuel of high anti-knockivalue is effected under conditions of highest over-all eiciency with minimum production of gas and deposition of coke and with a low requirement in apparatus.

It is a further object of the invention to providea method of treating crude oil or partially topped crude oil to convert it to motor fuel of high anti-knock value under the conditions outlined above. V

It is a further object of the invention to provide a novel and useful operating cycle for the treatment of crude oil having the above advantages and others which will be apparent from the following description.

The invention contemplates the separate treatment of a plurality of hydrocarbon oils of differing boiling ranges, which may be a light hydro*` carbon oil, for example, heavy naphtha, a heavyy hydrocarbon oil which may be reduced crude or w heavy gas oil and an intermediate hydrocarbon cil which may be a gas oil having a boiling range intermediate that of the said heavy hydrocarbon oil and said light hydrocarbon oil. The three hydrocarbon oils above mentioned may constitute the fractions produced from crude oil or partially topped crude oil by distillation. The crude oil may distilled by heating, for example, at a temperature of 500 to 800 F. at a pressure of 25 to 100 pounds per square inch and fractionating resulting vapors whereby the crude oil is divided into a reduced crude, for example, one having an initial boiling point of 650 to 750 F., a virgin gas-oil condensate, for example, one having an endpoint of 650 to 750 F., a heavy naphtha condensate, for example, one having an initial boiling point of 250 to 350 F. and an end peint of 450 to 550 F., and a light naphtha distillate. Instead of fractionating the crude oil to produce reduced crude it may be further distilled to produce a heavy gas-oil condensate having the same initial boiling point as the reduced crude, which heavy gas oil may be used instead of reduced crude in the invention, as set forth in the following description and specific example.

According to the invention the heavy hydrocarbon oil, for example, reduced crude, is subjected to cracking conditions of temperature and pressure to effect a relatively mild cracking of the oil to lighter products which include a substantial proportion of constituents above the motor-fuel boiling range. For example, a reduced crude may be heated to a temperature of 850 to 950 F. at a pressure of 75- to 400 pounds per square inch for a time sufiicient to eifect 10% conversion to motor-fuel constituents. The cracked products from the mild cracking or viscosity-breaking treatment of the reduced crude are separated into vapors and liquid residue. The separation is effected under conditions suitable to effect substantial vaporization of the cracked products whereby a heavy gas oil may be condensed from the vapors. This may be effected by the distillation of the hot products by application of heat thereto in the separating zone or by admixture therewith of highly heated hydrocarbon vapors from another source, for' example, from the reforming treatment of a heavy naphtha.

A light hydrocarbon oil which may be heavy naphtha produced by the distillation ofl a reduced crude is subjected to elevated conditions of temperature and pressure to eiiect reforming ofthe heavy naphtha to convert it to constituents of high anti-knock value. For example, the heavy naphtha may be heated to a temperature of 950 to l150 F. at a pressure of 500 to 1000 pounds per square inch for a time sufficient to effect the desired conversion. The hot products from such a treatment may be admixed with the products of the mild cracking or viscosity-breaking treatment of the reduced crude described above for separation of the cracked products into vapors and liquid residue in a common zone whereby the highly heated vapors 46 from the reforming treatment assist in thevaporization of the cracked products of the viscosity-breaking treatment.

The vapors separated from the products of the viscosity-breaking and reforming treatments are 60 fractionated to separate therefrom a heavy gasoil condensate, for example, one having an initial boiling point of 650 to 750 F., a low-boiling gas-oil condensate, for example, one having an end point of 650 to 750 F., and a naphtha dis- 65 tillate. The naphtha distillate is preferably fractionated to separate therefrom a heavy naphtha condensate and alight naphtha distillate.

The heavy gas-oil condensate is separately subjected to cracking conditions of temperature andpressure to effect a mild cracking of the heavy gasoil to lighter products including a substantial proportion of products above the motor-fuel boiling range. This cracking treatment preferably is somewhat more drastic thanthe treatment given the reduced crude because the clean, heavy condensate has less coke-forming tendency than the reduced crude. For eX- ample, the heavy gas-oil condensate may l-befA heated to a temperature of 900 to 1000" F. at 75 to 1000 pounds per square inch for a time sulficient to effect approximately 15% conversion to gasoline constituents. 'Ihe products of this cracking treatment are separatedl into vapors; and fbination with the separation and fractionation of the products of the reforming andV visbreaking operations.

.The lower-boiling gas-oil condensate separated from the products of the foregoing cracking operations is separately subjected to elevated conditions of temperature and pressure to effect conversion to lighter products including motor-fuel constituents. This operation may be carried out on a recycling basis whereby it is preferable to employ moderately drastic cracking conditions to` effect maximum conversion tomotor-fuel constituents of high anti-knock value consistent with minimum deposition of coke. For example, the lower-boiling gas-oil condensate andV recycle stock may be heated to a temperature of 900 to l1050" F. at a pressure of 200 to 1000 pounds per square inch for' a'time suflicient to effect 20% conversion to gasoline constituents. The products of this cracking treatment are separated into vapors and liquid residue, and the vapors are fractionated to separate a recycle stock and a desired distillate in separatory and fractionation Zones separate from those employed for the products of the previously described cracking operations. vSeparate separation and fractionation of these cracked products are advantageous since the naphtha distillate from this cracking vtreatment may be of relatively high anti-knock value and therefore would not require reforming.V It is thus preferably collected separately.

A clean hydrocarbon oil intermediate in boiling range between the heavy naphtha and the reduced'crude, which may be a virgin gas oil having an end point of 650 to '750 F. produced bythe said distillation of crude hydrocarbon oil, is separately subjected to elevated conditions of temperature and pressure to effect drastic cracking thereof to lighter constituents including' a substantial proportion of gasoline constituents of high anti-knock value. A hydrocarbon oil of this nature, especially a virgin gas oil, is particularly suited for drastic cracking treatment-on a oncethrough basis because of its low coke-forming tendency and relatively non-refractory nature. For example, the virgin gas oil may be heated t0 a temperature of 950 to 1100 F. at a pressure of 200 to 1000 pounds rper square inch for a time sumcient to effect a 35 to 50% conversion to gasoline constituents. The. products of the cracking treatment of the virgin gas oil are kept separate from the products of the cracking treati ment of the reduced crude and heavy gas-oil con- V'densate since the drastic cracking treatment of the virginv ga's oil produces a naphtha of high antiknockvalue which may not need reforming 4 treatment, The products may be separated in a zone `without admixture with other cracked products but conveniently may be treated in a common zone with the products of the cracking of the lower-boiling gas oil described above. In any case vapors separated from products of the cracking of the virgin gas oil are fractionated to separate a cycle gas oil which conveniently is admixed with the said lower-boiling gas oil 'for cracking treatment therewith.

The accompanying drawing is a diagrammatic view in elevation of apparatus suitable for carrying out the present invention. The invention will be further described in detail by reference to the drawing, but it is to be understood, however, that the invention is not limited by said drawing or by said specific description but is capable of other embodiments than those described and other embodiments which may be beyond the physical limitations of the apparatus illustrated.

Referring to the drawing, heaters I, 2, 3, 4, 5 and 6 are indicated, each provided with a suitable pipe coil for the treatment of hydrocarbon oils of differing characteristics at different conditions of temperature and pressure. For purposes of simplicity the heaters I to 6, inclusive, are indicated as separate structures. It is to be understood, however, that a plurality of these heaters may be combined in a singlefurnace structure wherein a plurality of coils, each of which performs the function of one of the heaters, is

mounted in the furnace in positions best suited for the heat treatment thereof necessary to effect kthe desired treatment of the hydrocarbon oil passing therethrough. For example, the functions of heaters I, 2 and 3 may be formed by a like number of coils located in a single furnace structure, and the -functions of heaters 4, 5 and 6 may be performed by a like number of coils located in a single furnace structure.

In addition to heaters I to 6, inclusive, crude ash tower 1, combined evaporator and fractionator 8, bubble tower 9, evaporator I0, fractionator I I, condensers I2, I3 and I4 and gasoline receivers I5, I6 and I'I are indicated together with auxiliary equipment for carrying out the process of the invention.

Heater I is provided for the preliminary heating of crude oil or partially topped crude oil which is introduced to the system through line I8 bymeans of apump I9 located in line I8. It is to b e understood, however, that the preliminarysheating lof the crude oil may be accomplished by any suitable heat exchange with hot products in the system in place of or in addition to the use of heater I, the use of which is shown merely for purposes` of illustration. In heater I the crude oil is heated under pressure and temperature conditions suitable to effect the desired distillation in crude flash tower 'I into which the heated crude is introduced through line 20 which is provided with avalveZI for any desired reduction' in pressure. For exampla'the crude may be heated to a temperature of 500 to 800 F. at a pressure of atmosphericto 100 pounds per square inch.

Crude ash towerr 1 is operated at a pressure of :atmospheric to 100 pounds per square inch,

and fractionation of the vapors from the distillation of the crude oil is* effected by maintaining the upper portionl of the tower at a temperature of 250 to 350 F. `The distilled crude oil separates into vapors vand liquidresidue in the lower portion of the tower 1, and a bottom temperature of 650 to 750`F. is maintained to effect the desired distillation. 'Trap-out trays 22 and 23 are provided in tower 1 above the point of introduction of the heated crude to collect a heavy naphtha condensateand a yvirgin gas-oil condensate, respectively. The heavy naphtha condensate collected in trap-out tray 22 maybe one having an initialboiling point of 250 to 350 F. and an vendpoint of 450 to 500 F. The virgin gas-oil condensate collected in'trap-out tray 23 maybe one having an end point of 650 to 750 F.

The reduced crude collected in the bottom of tower 1 may be used for further treatment as such or may be further distilled to separate therefrom a heavy gas oil which may be employed for further` treatment in place of the reduced crude. For purposes of illustration, however, the

invention is described as applied to the treatment, of a reduced crude obtained in the above manner. i A

Reduced crude from the bottom of tower 1 is withdrawn throughline 24 provided with a pump 25 and introducedinto vvheater 2. In heater 2 the reduced crude is subjected to relatively mild and conversion thereof 'to' constituents of im-' 7.5; oil condensate, for-example, one having, an initial cracking conditions to effect conversion to lower` ,i duced crude but above the motor-fuel boiling range. For example, thereduced jcrude may be heated in heaterV 2 toa temperature of 850 to 950 F.l at a pressure of `'75 to 400 pounds" per square inch fora time sufficient to effect the desired conversion. The cracked products from heater 2 are withdrawn therefrom through line 26 provided with a control valve 21 and introduced into the lower or evaporator portion `of tower 3 for separation into vapors and `liquid residue.

Heavynaphtha is withdrawn from trap-out tray 22 through line 28 provided with pump 29 and introduced into heater 6 wherein it is subjected to elevated conditions of temperature and pressureto effect reforming of the heavy'naphtha proved anti-knock value. For example, the heavy naphtha may bel heated in heater 6 to a te'mpera-` ture'of 950 to21150 F. at a pressure of` 500 to` 1000 pounds per square inch for a time sufcient' lto effect thefdesired reforming treatment. The

hot reformed 'products are withdrawn from' heater 6 through line 30 provided with a control valve 3| and introduced into the evaporator por` 65, tion of tower 8 preferably lby introduction into.v transfer line 26 whereby the Volatile hot products' duced therein and the condensation, in the upper or fractionator portion thereof, of a heavy gas' bolingpoint of 650." to 750 F; Fractionation is obtained by maintaining the top of the tower 8 at a temperature suciently low to permit passage overhead of products boiling at 650 to '150 F. and lower. For example, tower 8 may be operated at a pressure of 10 to 200 pounds per square inch at a top temperature of 550 to 700 F. and a bottom temperature of 600 to 800 F. A trap-out tray 32 is provided in tower 8 at an intermediate portion thereof for the collection of the heavy gas-oil condensate and to separate the tower 8 into a lower or evaporator section and an'upper or fractionator section.

Heavy gas-oil condensate is withdrawn from trap-out tray 32 through line 33 provided with a pump 34 and introduced into heater 3 wherein it is subjected to relatively mild or viscositybreaking cracking conditions of temperature and pressure toeect conversion to lighter products including a substantial proportion of constituents above the motor-fuel boiling range. In heater 3 the heavy gas oil is subjected to relatively more drastic cracking treatment than the crude oil in heater 2 because of the lesser coke-forming tendency of the clean heavy gas-oil condensate. For example, in heater 2 the heavy gas-oil condensate may be heated to a temperature of 900 to 1000F. at a pressure of '75 to 1000 pounds per square inch for a time sufficient to effect the desired conversion. The cracked products from heater 3 are withdrawn through line 35 provided with control valve 36 and introduced into the evaporator section of tower 8 conveniently by admixture with the cracked products in transfer line 26 whereby the hot reformed products from line 38 assist also in the vaporization of the products of the cracking treatmenti of the heavy gas-oil condensate. e e

A relatively heavy tar is withdrawn from the lower portion of tower 8 through line 31 provided with valve 38 for treatment elsewhere, for example, as fuel. When tower 8 is operated under substantial pressure the tar withdrawn through line 31 may be treated in a separate evaporator tower, not shown, to vaporize light constituents contained therein which may be recovered as condensate and returned to the upper part of tower 8 as reflux.

The vapors uncondensed in tower 3 pass overhead through line 39 provided with valve 40 and areintroduced i'nto bubble tower 9 wherein they are fractionated to separate a gas-oil condensate lower boiling than the heavy gas-oil condensate separated in tower 8, a heavy naphtha condensate and a light naphtha distillate which passes overhead. The desired fractionation is accomplished by maintaining the top of tower ,9 at a temperature of approximately 300 to 400 F. at a pressure of 10 to 200 pounds per square inch. The bottom temperature may be maintained at 500 tof700 F. to effect the desired separation. A trap-out tray 4I is provided at a suitable point for the collection of a heavy naphtha condensate which may be withdrawn therefrom through line 42A provided with a valve 43 and introduced into line 28 for passage' to the reforming heater 6 for treatment therein.

The said lower-boiling gas-oil condensate is withdrawn from the bottom of tower 9 through line 44 provided with a valve 45 and a pump 46 and introduced into heater 4 wherein it is subjected to moderately drastic cracking conditions of temperature and pressure to effect conversion to lower-boiling products including motor-fuel constituents. For example, the low-boiling gas "'ucts from heater 5 are withdrawn therefromy fuel constituents.

oil inheater 4 may'be'heated to ja temperature of 900 to 1050 F. and a pressure of 200 to 1000 pounds per square inchffora time suicient to `effect the desired conversion. The hot productsy i. from the cracking treatment in heater 4 are withdrawn therefrom through line 41 and provided With lvalve I8 and introduced into evaporator l lfor separation into vapors and liquidl residue;

flvaporator I0 is maintained under temperature and pressure conditions effective to cause. vaporization of constituents suitable for further cracking treatment and lighter products, for example, all constituents boiling-.at 650 to '750 F.

or lower. yEvaporator E0 may be maintained at a pressure of l0 to 200 pounds per square inch to a bottom temperature of 600 to 800 F. The vapors separated are withdrawn from the-.upper portion of evaporator I0 through line 48 provided with a valve `5l) andintroduced into fractionator il. i

In fractionat'or II thevapors introduced are fractionated to separate a reux condensate and a desired distillate which consists of a gasolinel fraction 'and lighter products.

For example, to eifect the desired fractionation fractionator II may be maintained at a pressureA of to 200 pounds per square inch with a top temperature of approximately 300 to 400 F. and a bottom temperature of 500 to '100 F.` The reflux condensate collected in the bottom of fractionator II is withdrawn therefrom through line 5I provided with avalve 52. Line 5I preferably connects with line G4 whereby the reflux condensate is returned for further cracking treatment in heater 5i, but it is to be understood that other and separate treatment of the reflux condensatemay be eected.

The liquid residue which collects in the bottom of vevaporator I0 is withdrawn therefrom throughv line 53 provided with a valve 54 for use elsewhere,

for example, as fuel. When evaporator III is op-v.

23 throughline 54 provided with a pump 55 and 'introduced into heater 5 wherein the virgin gas oil is subjected to drastic crackingconditions of temperature and pressure to eifect a substantial conversion of the oil to lighter products including substantial proportions of high anti-knock motor- For example, the virgin gas oil be heated in heater 5 toa temperature or 950 to ll00 F. at a pressure of 200 tol000 pounds per square 'inch for a'time suflicientto eTect the desired conversion. The cracked prodthrough line provided with control valve 51. Line 56 connects with transfer line 41 from-heater l whereby the hot products of heater 4 and heater 5 are passed together to evaporator I0, and the cracked products from heater 5 are `treated in` evaporator I0 and fractionator II together with those from heater d in the manner described above.

Naphtha distillates unconclensed in towers 1,`

' 9v and it are withdrawn therefrom` through lines 58, 50 and respectively, provided with valves 5I, 02 and 03. C'ondensers l2, I3 and I4 are provided in lines 58, 59 and 60, respectivelyVfor effecting liquefaction of the gasoline constituents whichtare separated from accompanying gases in receivers I5, i6 and I1. Gases thus separated are .withdrawn from the reecivers through lines 64, and 66 provided with control valves 61, B8 and 69, respectively. The gasolines thus separated may be Withdrawn separately from the receivers through lines 10, 1I and 12 provided with valvesv 13, 14 and 15, respective1y, or by means of line -16 which connects with receiver.l5 and lines 18 and 19 which connect receivers I6 and I1, respectively, with line 16. Any desired blend of the gasolines produced in the' system may be effected by suitable manipulation of valves 11, and 8| located in lines 16, '18 and 19, respectively. v

-Cooling means such as freux means or cooling coils 82, 83, 84'and 85 may be provided in the upper portion of towers 1, 8, 9 and I I, respectively, to effect desired fractionation therein. Auxiliaryheating means such as heating coils 86, 81,

88,89--and 00 may be provided in the lower portions of towers 1, 8 and 9, evaporator I0 and fractionator II, respectively, to assistin maintaining the desired temperatures at those places.

The hot products passingv through transfer lines 26, 30, 35, 41 vand 56 may be-suitably cooled, if desired, by heat exchange or by the admixture therewith of suitable cooling fluid prior to introduction into the respective separating zone, by means notshown.

Towers 1, 8, 9 and II are provided with suitable gas and liquid contact means to facilitate the absorption, condensation, stripping and evaporation which comprises fractionation. It is evident that the functions of the towers could be performed by a fewer number, but the arrangement shown is for purposes of simplifying the illustration of the'invention.k For example, towers 8 and 9' could be combined in a single structure performing the functions of both'.

In the apparatus villustrated no means is provided for disposing of materials collected in trapout trays 22, 23, 32 and 4I and in the bottoms of vtowers 1, 9 and II other than for their further use inthe system. It is to, be understood, however, that the proportions of these intermediate products to -be used may vary depending' upon the quality of the raw material' and the 'results desired. Separate means not shown may be provided for withdrawing portions of these intermediate products from the system, and it is to be understood that the invention is not limited to a process wherein all of each intermediate `product is returned to the system.

According to la' preferred modification of the invention a reduced crude, for example, one having an initial boiling point of 650 lto '150 F.'is heated in heater 2. to a temperature of approximately 880 F. at a pressure of approximately 200 pounds per square inch for a time sufficient to effect 10% conversion to gasoline products, and the cracked Vproducts are then` passed through line 26 to the evaporator portion of tower 8. Heavy naphtha from trapout trays 22 and 4I is heated in heater Grito-.a temperaturel of apa temperature of approximately 950." F. at a pressure ofabout 400 pounds per square inchforV a timesufhcient to effect conversion to gasoline constituents, andthe cracked products are lintroduced into tower 8 for separation and fracend point of 650 to 750 F. which collects at the bottom of tower 9 and a naphtha distillate which passes overhead. The gas-oil condensate from the bottom of tower 9, together with cycle stock from the bottom of tower Il, is heated in heater 4 to a temperature of approximately 990 F. at

a pressure `of about 400 pounds per square inch to eiect approximately conversion to gasoline constituents.

Virgin gas oil from trap-out tray 23 is heated in heater 5 at a temperature of approximately 1010 F. at a pressure of about 750 pounds per square inch for a time sufficient to effect V35 to 50% l conversion to gasoline constituents.

,The cracked products from heaters 4y and 5 are separated in evaporator linto vapors and liquid residue. The vapors pass overhead into fractionator Il wherein a reflux condensate is separated and naphtha distillate passes overhead.

The present invention thus provides a method of treating crude oil or reduced crude to convert it to gasoline of high anti-knock value wherein the various fractions separated from the crude oil and intermediate products prepared therefrom are each treated under optimum conditions to effect -maximum conversion to gasoline of high anti-knock value under conditions of maximum efficiency and minimum formation of gas and deposition of coke. The operation of heaters 2 and 3 represents a two-stage treatment of the heavier constituents of the crude oil to effect maximum conversion to constituents suitable for further conversion with minimum production of gas and deposition of coke. The cracked products from these operations are relatively heavy whereby it is advantageous to admix therewith the hot products from the reforming treatment of the virgin naphtha to effect the desireddegree of vaporization ofthe cracked products whereby a cycle stock for heater 4 may be obtained in trap-out tray 32. The vapors from this separation of cracked products are separately fractionated to obtain a lighter gas-oil 'cycle stock and a heavy naphtha for reforming treatment since the naphtha resulting from the mild cracking treatment of the reduced crude and heavy gas oil is ordinarily of low anti-knock value. On the other hand, the operation of heater 4 on a recycling basis and operation of heater 5 on a once-through basis effect maximum production'in each case of high anti-knock naphtha consistent with minimum deposition of coke and formation of gas by the stocks treated. The vapors from these cracking operations are therefore separately fractionated since ordinarily no reforming of the naphtha is necessary. Heater 4 is operated under less drastic conditions than heater 5 since the feed therefor is ordinarily more refractory than the fresh feed for heater 5. The cycle stock recovered from the products of cracking in heater 5, however, is of a more refractory nature than the fresh feed from which it is obtained, and the cycle stock is therefore conveniently recovered with that from the cracked products from heater 4 for recycling to heater 4 for treatment therein.

These and many other advantages are apparent from the foregoing description which has been given for the purpose of illustrating the invention. It is to be understood, however, that the invention is not limited to the specific embodiments described or the apparatus illustrated but is capable of other embodiments which may be beyond the physical limitations of the apparatus indicated in the drawing.

I claim:

l. The method of treating hydrocarbon oils to produce therefrom lighter hydrocarbon oils ncluding motor fuelV constituents which comprises separating crude petroleum into vapors and residue in a primary separating zone and fractionating the separated vapors in a primary fractionatmg zone to form virgin gas oil and naphtha condensates, passing resultant residue to a singlepass viscosity-breaking zone wherein the residue is subjectedto cracking conditions of temperature and pressure under viscosity-breaking conditions to effect conversion into lighter products including a substantial proportion of constituentsr above the motor fuel boiling range, delivering the resultant viscosity-broken products into a second separating zone, passing virgin naphtha condensate from the primary fractionating Zone to a separate reforming zone wherein the `naphtha is subjected to cracking temperature adequa'te` to effect conversion of gasoline constituents into components of increased anti-knock quality, discharging the resultant reformed products atY cracking temperature into. said second separating zone to aid in effecting the separation of the viscosity-broken products into vapors and residue, passing the separated vapors from the second separating zone to a second fraction- `ating Zone wherein the vapors are subjected to fractionation to form heavy gas oil, lighter gas oil and naphtha condensates, directing heavy gas oil condensate from the second fractionating Zone to a recycling cracking Zone wherein it is subjected to cracking conditions of temperature and pressure to effect conversion into lower boiling products including a substantial proportion of constituents above the motor fuel boiling range, passing the resultant lcracked products from said recycling cracking zone to said second separating zone wherein said cracked products are subjected to Vaporization with the aid of the hot products from the reforming Zone, passing virgin gas oil from the primary fractionating zone to a separate single-pass gas oil cracking Zone wherein it is subjected to high cracking temperature under superatmospheric pressure and under conditions of high cracking per pass to eiect conversion into motor fuel constituents of high anti-knock quality, directing lighter gas oil condensate from the second fractionating zone to a second recycling cracking Zone wherein the oil is subjected to cracking conditions of temperature and pressure to effect conversion into motor fuel constituents, separating into vapors and residue thecracked products from the single-pass gas oil cracking zone and from the second recycling cracking zones externally of the separating and fractionating Zones hereinbefore mentioned, fractionating the separated vapors in a third fractionating zone to form a desired distillate and reflux condensate and cycling reflux condensatev from the third fractionating zone to the latter recycling cracking zone.

2. The method of treating hydrocarbon oils to produce therefrom lighter hydrocarbon oils including motor fuel constituents which comprises separating crude petroleumA into vapors and residue in a primary separating zone and fractionating the separated vapors in a primary fractionating Zone to form virgin gas oil and naphtha condensates, passing resultant residue to a single-pass viscosity-breaking zone wherein the residue is subjected to cracking conditions of temperature and pressure under Viscosity-breaking conditions to effect conversion into lighter products including a substantial proportion of constituents above the motor fuel boiling range, delivering the resultant viscosity-broken products into a second separating zone, passing virgin naphtha condensate from the primary fractionating Zone to a separate reforming Zone wherein the naphtha is subjected to cracking temperature adequate to effect conversion of gasoline constituents into components of increased antiknock quality, discharging the resultant reformed products at cracking temperature into said second separating zone to aid in effecting the separation of the viscosity-broken products into vapors and residue, passing the separated vapors from the second separating Zone to a second fractionating zone wherein the vapors are subjected to fractionation to form heavy gas oil, lighter gas oil and naphtha condensates, directing heavy gas oil condensate from the second fractionating zone to a recycling cracking zone wherein lit is subjected to cracking conditions of temperature and pressure to effect conversion into lower boiling products including a substantial proportion pf constituents above the motor fuel boiling range, passing the resultant cracked products fromrsaid recycling crackingA zone to said second separating zone wherein said cracked products are subjected to vaporization with the aid of the hot products from the reforming zone,l

passing virgin gas oil from the primary fractionating zone to a separate single-pass gas oil' cracking Zone wherein it is subjected-to high cracking temperature under superatmospheric pressure and under conditions of high cracking per 'pass' to eect conversion into motor fuel constituents of high anti-knock quality, directingv lighter gas oil condensate from the second fractionatingzone to a second recycling cracking zone wherein the oil is subjected to cracking conditions of temperature and pressure to effectccnversion into motor fuel constituents, directing the resultant cracked products from the'single-pass gas oil cracking zone and from the second recycling cracking zones toa third separating zone wherein separation of vapors from residue takes place, passing the separated vapors tol a third fractionating zone wherein the vapors are fractionated to form a desired distillate and reflux condensate and cycling reux condensate from the third fractionating zone to the latter recycling cracking zone. i

3. The method in accordance with claim 1 wherein Viscosity-breaker naphtha condensate from the second fractionating zone is combined with virgin naphtha condensate fromthe primary fractionating zone for passage to the said reforming zone.

WAYNE E. KUHN. 

